I found the exact problem with my engine after years of driving it. No idea who built this engine. It didn't cause any problems but I corrected it once I found it. Just check for any signs of wear damage that might cause issues.
I used a camera bore scope to inspect things and I've rotated the engine to visually check for wear also.
I had some misfire at idle develop and that lead to this teardown. I've had the push rods out and check the lifters also.
The timing chain slack seems to be the issue. I could rotate it 10 degrees before the rotor began moving. rotating slowly to measure the play in the chain.
Ill be fixing the rocker shafts as I wait for parts.